1. Field of the Invention
The present invention is related to auxiliary telephone equipment and, more particularly, is directed towards a security system which may be adapted to be connected to standard dial or push-button telephone instruments for preventing long distance calls by anyone other than an authorized user.
2. Description of the Prior Art
The prior art is replete with both electrical, electronic and mechanical devices for preventing an unauthorized person from placing long distance calls on a telephone. Prior art U.S. patents in this area of which I am aware include: U.S. Pat. Nos. 3,284,578; 3,513,271; 3,757,055; 3,851,109; 3,872,260; and 3,973,083.
The McCann et al. patent (U.S. Pat. No. 3,757,055) is exemplary of many prior art systems in teaching a long distance call inhibitor which utilizes a counting circuit to count the number of digits dialed and causes the telephone lines to be opened when that count reaches eight. An alternative logic circuit is also provided which causes the telephone line to open whenever the digit "0" is among the first three digits dialed. This circuitry is typical of many prior art systems which simply disable the telephone when anyone attempts to place a long distance call.
The Oatis patent (U.S. Pat. No. 3,872,260) teaches another type of toll call prohibitor which detects removal of the receiver from a telephone instrument and also includes a series of counters which are programmed to count pulses derived from the make and break of the instrument dial, and means for determining the number of dial pulls in cooperation with a disallowed number detector for disconnecting the telephone upon detection of an unauthorized number being dialed.
The Stathacopoulos patent (U.S. Pat. No. 3,513,271) teaches circuitry which disables the telephone upon detection of the initial digit of a long distance code, such as a "0". This system includes mechanical switches which are operable by a locking cam which, in turn, is controlled by the manual turning of a key to permit an authorized user to disable the toll call inhibiting system.
The Sekiguchi patent (U.S. Pat. No. 3,973,083) discloses another type of toll call inhibitor which senses whether the number "1", the number "0", or one of the numbers "2" through "9" are dialed. This circuitry acts to disable the telephone when either the initial number is "0" or the first or second numbers are "1".
The Downs et al. patent (U.S. Pat. No. 3,851,109) discloses a system which interrogates dialed digits to determine if the dialed sequence is to be allowed or disallowed as a function of pre-programmed instructions. This patent contains a good description of the prior art in columns 1, 2 and 3.
Finally, the Evans patent (U.S. Pat. No. 3,284,578) illustrates an early electro-mechanical device which detects whether the second digit of an area code is a "0" or a "1", upon which the dial mechanism is locked to prevent further operation.
Each of the devices described in the foregoing patents suffers from a common deficiency. While teaching a multitude of different approaches for disabling the telephone when an unauthorized long distance call is attempted, none of the references incorporate a simple, foolproof, electronic system which permits an authorized user to overcome the disabling system. The closest prior art patent of which I am aware in this regard is Stathacopoulos (U.S. Pat. No. 3,513,271), but as pointed out above, this device requires insertion of a key to actuate a plurality of switches to overcome the toll call inhibiting device. As is well known, any security system which is key-operated may be easily defeated either mechanically, by force (disassembly of the key switch), or by one who through whatever means can come into possession of a key which turns the lock. Such systems are therefore severely deficient with respect to their true security capabilities.
It is towards overcoming the above-noted disadvantage that the present invention is advanced.